This invention relates to an apparatus for the simulative optimalization of the supporting of a sheet metal blank on the support frame of a deep-drawing tool.
The drawing of vehicle body parts in deep-drawing presses can be subdivided into four phases, namely:
1) insertion of the blank; PA0 2) closing of the blank holder and application of the hold-down force; PA0 3) lowering of the punch and the actual drawing operation; and PA0 4) opening of the tool and removal of the drawn part.
Apart from the actual drawing operation, which has been very often discussed in the literature, the other two preceding phases also affect the quality of the drawn part. In good deep-drawing tools, the bottom drawing frame and the hold-down device fitting it with a matching shape must be so designed that the blank, after it has been placed on the bottom drawing frame, can be pressed by the hold-down device against the support surface of the bottom drawing frame over the full area without forming wrinkles. In connection with this, it should be borne in mind that the support surface of the drawing frame is usually by no means flat, but already approximates the three-dimensional contour of the finished drawn part. The blank clamped between the drawing frame and the hold-down device should, in addition, be spatially twisted into a shape such that the point of first contact of the descending drawing punch with the blank should lie approximately in the middle of the blank.
The prior art attempts to obtain a utilizable shape of the support surface of the drawing frame, or of the hold-down device, with development tools made of a sufficiently loadable but easily workable modeling material, such as, for example, plaster, synthetic resin or combinations of wood and plastics. This involves a tedious and cost-intensive iteration process using the "trial and error" approach. An additional difficulty is that the blank clamped in position at the edge in this manner is completely out of sight, and that any wrinkling can be seen only after the development tool has been opened. By drawing conclusions from the shape and position of the wrinkles, and on the basis of long experience, the drawing frame and the hold-down device must then be modified and a new edge clamping arrangement tested.
The development tool corresponds in each case to a specific drawn part on the scale of 1:1 and, after completion of the development of the drawing frame or hold-down device specific to the drawn part concerned, is used in its actual size for making the drawing tool suitable for production. Since for the production of a vehicle body many different drawing tools have to be developed and made available, a large amount of time is taken up solely for the development of the numerous different drawing frames before production can start.
The problem underlying the invention is that of making available a means for enabling such drawing frames or hold-down devices specific to drawn parts to be developed with optimum shapes in a shorter time and at lower cost than hitherto.
According to the invention, this problem is solved by the apparatus for the simulative optimalization of the supporting of a sheet metal blank on the support frame of a deep-drawing tool, comprising a flat, horizontally aligned base plate, which in both length and breadth is larger than the largest sheet metal blank to be studied; a plurality of stands freely translatable and rotatable about a vertical axis and capable of being fixed on the base plate in any desired position in respect of translation and rotation; wherein each stand carries a mouth-like clamp which by means of appropriate mountings can be turned and fastened about two horizontal pivot axes at right angles to one another, and which by means of a fastenable vertical guide can be vertically adjusted and fastened on the stand; and further, wherein each clamp contains on the bottom inside face of the mouth opening a support part-surface which forms a partial region of a support surface to be simulated for the sheet blank, and, lying opposite the support part-surface in the mouth opening, a clamp jaw translatable in parallel transversely to the support part-surface and capable of being pressed with a defined force against the support part-surface.
With the aid of a plurality of clamps adjustably fastened on stable stands, the drawing frame and the hold-down device can be simulated area by area and varied in a simple, rapid manner. In addition, the blank clamped at its edge is always within sight, so that the formation of wrinkles when the edges are clamped can be viewed directly. The shape of the edge clamping can even be varied while the blank is clamped in position, so that the action of variations of the shape of the edge clamping on any wrinkles formed can likewise be viewed directly. The optimum shape of the edge clamping can thus also be quickly found without trial pressings.
In order to be able to check whether the drawing punch actually makes its first contact with the clamped blank in the middle, it is sufficient to lower a part of the drawing punch, or a hand specimen of the finished component, in a defined position. The situation of the first point of contact can be seen visually by side viewing and can also be determined by making reference marks.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.